Searching for Wood Thrushes

"Little thrushes should be heard but not seen"?

(Listen to the radio version here.)

One of the many wonderful things about birding is how it can be enjoyed in solitude, with one or two others, or as a group. A lot of the time, I like to be entirely alone when I’m out there, but sometimes it’s more fun to have company.

On Tuesday morning, June 4, I went birding with my good friend Michael Bernstein. One of the things that make him an excellent birding companion is that he doesn’t get the least bit antsy when we’re hearing a bird who stays hidden for over half an hour. He works just as hard as I do (and even more effectively, with his significantly younger eyes and ears) to find it.

Bernie turned out to be a real asset when we were at a lovely picnic spot at Waabizheshikana—the wonderful place near the zoo in West Duluth that I used to call the Western Waterfront Trail—and we heard a Wood Thrush singing.

My parents used to tell us that “children should be seen but not heard.” Apparently, Wood Thrushes receive the opposite advice. They have one of the richest, most gorgeously complex of bird songs, but like other thrushes, they stay well concealed, avoiding our prying eyes.

I heard my first Wood Thrushes several times in May 1975 when I was birding alone in East Lansing, Michigan, and a month later during my first ornithology class in Kalamazoo, but I couldn’t find even one, so I didn’t add it to my life list until I finally saw one in Scott Woods in East Lansing a year later.

Since then, I’ve found Wood Thrushes in quite a few places throughout the eastern states and Ontario, and in Costa Rica in winter, but I haven’t seen nearly as many as I’ve heard. The best I ever did as far as seeing them was when I lived in an apartment complex surrounded by deciduous woods in Ithaca, New York, while I was working at the Cornell Lab of Ornithology, the first year I had a good digital camera with a telephoto lens. I heard Wood Thrushes practically every time I walked my dog Photon in late spring and early summer—that was three or four times a day—and I almost always brought my camera. Photon was exceptionally cooperative when I was looking for birds, but in all those weeks, I got a glimpse of a Wood Thrush only a handful of times and managed to click a photo or two on just three of those walks.

The best, or at least the closest, photos I’ve ever taken of Wood Thrushes were not of singing birds, but of one in the hand at the banding station at Braddock Bay Bird Observatory on Lake Ontario in Upstate New York in 2009 …

… and one taking a siesta under the boardwalk at Magee Marsh in Ohio last year, during the birding festival known far and wide as the Biggest Week in American Birding.

Since we moved to Duluth, Wood Thrushes have been very hard for me to come by. I never saw or heard one on Peabody Street until May 18, 2021, a full 40 years after we moved here. Early that morning, I’d set out my recording equipment in the back of my yard, and when I went out at mid-morning to stop the recording, I heard a Wood Thrush in the woodsy area behind my yard. I moved my recorder much closer to where the sound was coming from, ran in to get my camera, and searched every branch I could see as the bird sang away. I could not find it, and less than four minutes after I started that new recording, a dog walker talking loudly on a cell phone passed by, scaring the bird off. I got a glimpse of the thrush flying away, but no photos. But that night, when I ran through the photos from a trail cam that had been focused on my bird bath, there was a picture of the Wood Thrush, hunting in the grass. It’s poor quality and very cropped, but I was thrilled to have a picture of my very first Peabody Street Wood Thrush to go with my 3-minute recording.

Minnesota is at about the extreme northwest of the Wood Thrush range.

A typical 25-mile Breeding Bird Survey here averages less than one Wood Thrush per survey route, compared to 19 of them per route where they’re most abundant, in the Appalachian Mountain Region. A major study conducted across the species’ breeding range found 53 percent of nesting areas were in deciduous forests, 45 percent in mixed forests, and only 1 percent in coniferous forests.

Wood Thrushes feed on invertebrates in the relatively cool, moist soil beneath dead leaves, and the single most important feature of a woodland where Wood Thrushes thrive seems to be a well-developed layer of leaf litter. Unfortunately, invasive species of earthworms quickly break leaf litter down. This is one important factor in why Wood Thrush populations have declined precipitously since the Breeding Bird Survey began keeping track of them in the 1960s.

Forest fragmentation is another. Wood Thrushes nest in large, contiguous forests and also in small woodlots. But they enjoy significantly greater nesting success in larger forests because those nesting anywhere near the edge of a forest lose so many young to cowbird parasitism. (Cowbirds seldom go deep into any forest.)

Another major factor in the decline of Wood Thrushes has been acid rain, which leaches calcium from the soil, making it less available for the soil invertebrates that Wood Thrushes eat. This in turn has led to eggshell thinning, which grows worse as soil acidity increases. The Breeding Bird Survey map for Wood Thrushes, which shows the patterns of population increases and decreases over the continent, shows some of the worst declines in the Northeast where, not coincidentally, acid rain has been worst.

Map showing Wood Thrush population trends based on Breeding Bird Atlas data from 1966-2015. Red and orange show areas of decline; light and dark blue show areas where the population has increased.

Acid rain is mostly caused by sulfate emissions from coal plants, and since the federal government started enforcing the Clean Air Act by mandating scrubbers (which of course the fossil-fuel industry opposed strenuously), the problem has decreased. Breeding Bird Survey numbers have shown a recent small increase, continent-wide, pretty well corresponding to the decline in acid rain thanks to those scrubbers.

Wood Thrush populations over the Breeding Bird Survey range are nowhere near the levels they were a half century ago, but at least are currently on the upswing.

Minnesota is one of the few places where Wood Thrushes haven’t been declining, not because our power plants were doing things right to begin with, but because prevailing wind patterns carried so much of the sulfur dioxide our plants emitted further east.

Meanwhile, steadily warming temperatures coupled with drought and high winds have been killing off many conifers in our part of the country.

Warming temperatures and drought conditions have taken a toll on black spruce and hemlock trees in the Sax-Zim Bog. I took this photo last summer.

At the same time, deciduous hardwood trees have been extending their range north. Here in Minnesota, the expansion of the hardwood trees spells good news, at least locally, for some birds dependent on the eastern deciduous forest, such as Red-bellied Woodpeckers, Yellow-throated Vireos, and Wood Thrushes. In the past few years, people have even been reporting Wood Thrushes regularly in the Sax-Zim Bog.

Waabizheshikana, where Bernie and I were searching for our singing Wood Thrush, has been lovely deciduous woods all along. I regularly see and hear Red-bellied Woodpeckers there, and often Yellow-throated Vireos, but never before have I had a Wood Thrush. We couldn’t spot him, and when Bernie left the main path to follow a smaller path closer, I pulled out my cell phone to get a few recordings, starting at exactly 9:55 am, several minutes after we first heard it.

• Wood Thrush recording: 4 songs (48 seconds)

• Wood Thrush recording: 9 songs ( 74 seconds)

• Wood Thrush recording: 11 songs, with the interval between songs shortened (47 seconds)

Bernie finally located the singer and got me on him in time to take a few photos at 10:22, but the camera focused on the branches in front of the bird, and within a few seconds, he was gone.

I kept searching since the bird was still singing so persistently and Bernie was being so obliging, and at 10:36, voila! There he was, even closer, on the other side of the path. (The reason I know the times so precisely is because my camera and phone record that data.)

A branch crossed right in front of him, so any professional bird photographer would have taken a few steps to the left or the right, but I’m just a birder with a camera and didn’t want to risk spooking him. The photo looked the way the bird did, and for me, that was mission accomplished! When he moved again, we left him singing the way he wanted to—unseen.

Scientists know of at least two functions of Wood Thrush songs—to declare and defend a territory and to attract a mate. Larry and Jan Kraemer had reported on eBird a Wood Thrush in the same area on June 2, so I’m pretty sure this is, at least temporarily, his territory. But it was impossible to determine whether he had a mate or was still trying to attract one. We’ll need to see two birds simultaneously, see one while hearing another, or see evidence of young to be sure. If he doesn’t lure a mate here, he’ll move on, if he hasn’t already.

I returned three days later with my grandson Walter, arriving at the Wood Thrush spot in late morning.

Someone was dressed for mosquitoes and puddles. We lucked out as far as both went—few mosquitos and plenty of puddles!

My companion this time wasn’t quite as focused on birds as I was. I listened hard and turned on my phone’s Merlin app in case I was too distracted or the bird too far away for me to detect, but no luck.

That doesn’t mean he’s gone—most birds take a break from singing in midday, so I’ll have to keep checking. Meanwhile, I’m sure happy to have my photos and recordings, mementoes of a lovely morning with a good friend and a splendid bird.